Personality differences from intra‐cortical myelin levels

I’ve always wondered why a physical defect of connective tissue, as we have with EDS, is linked to anxiety (my life’s greatest plague after pain). This article shows that a lack of good insulation (myelin) around brain neurons can lead to distinct negative personality traits.

Researchers are getting closer to understanding the neurological basis of personality. For a new paper in the Journal of Personality, Nicola Toschi and Luca Passamonti took advantage of a recent technological breakthrough that makes it possible to use scans to estimate levels of myelination in different brain areas (until fairly recently this could only be done at postmortem).

This makes me wonder if our defective connective tissue might also lead to defective insulation around our neurons, allowing some signals to “leak” to adjacent areas. Could that explain my general “mood instability” as well?

The new findings, though preliminary, suggest that people with “healthier”, more advantageous, personality traits, such as more emotional stability and greater conscientiousness, may benefit during development from more enhanced myelination in key areas of the brain where the myelination process is particularly prolonged in humans, continuing through adolescence and into the twenties.

The findings are based on brain scans of over 1000 young men and women (average age 29) who also undertook a personality test tapping the “Big Five” traits.

Averaged across the entire sample, the researchers found a pattern of myelination through the cortex that closely matched the pattern first discovered over a hundred years ago (from investigation of post-mortem brains) by the German neuroanatomist Paul Flechsig – see image above.

the researchers found several links between personality traits and myelination.

For instance,

lower emotional stability (i.e. higher neuroticism) was correlated with less myelination in the prefrontal cortex, a key brain region for emotional control;

higher agreeableness was correlated with greater myelination in orbitofrontal cortex (specifically in the anterior region, previously implicated in prosocial behaviour); and

higher conscientiousness correlated with greater myelination in part of the prefrontal cortex (the prefrontal cortex pole, which is associated with the human conscience, among other functions).

The aforementioned correlations suggest a straight-forward pattern whereby what we would usually consider as more advantageous traits are associated with greater myelination in key brain areas.

Broadly speaking, the findings “improve our understanding of the neurobiological underpinnings of variability in common behavioral dispositions” Toschi and Passamonti wrote.

Summarising their results, they added that “The personality‐related variability in the intra‐cortical myelin content … represent[s] an important proxy measure of the underlying neurodevelopmental mechanisms that shape subject‐specific attitudes in cognitive, emotional, and behavioral functions”.

Conclusions

Intra‐cortical myelin levels in brain regions with prolonged myelination are positively associated with personality traits linked to favorable outcome measures. These findings improve our understanding of the neurobiological underpinnings of variability in common behavioral dispositions.

I learned that there are three layers of connective tissue surrounding each nerve:

Endoneurium. Each nerve axon or fiber is surrounded by the endoneurium, which is also called the endoneurial tube, channel or sheath. This is a thin, delicate, protective layer of connective tissue.

Perineurium. Each nerve fascicle containing one or more axons is enclosed by the perineurium, a connective tissue having a lamellar arrangement in seven or eight concentric layers. This plays a very important role in the protection and support of the nerve fibers and also serves to prevent the passage of large molecules from the epineurium into a fascicle.

Epineurium. The epineurium is the outermost layer of dense connective tissue enclosing the (peripheral) nerve.

It seems to me that having defective insulation around nerves could certainly lead to the kind of instability we see with EDS. However, I’m not sure how Myelin relates to these three layers.

Continued from the full study:

The main aim of this study is to explore the interesting but as yet unaddressed question of how inter‐individual differences in personality traits relate to the intra‐cortical myelin content, especially in those brain regions which are known to mediate individual differences in personality traits (i.e., prefrontal and temporo‐parietal cortices)

For example, epidemiological and psycho‐sociological studies in large cohorts of people across the life span have found that some personality profiles relate to more “mature” behavioral patterns in terms of

emotional (low Neuroticism),

cognitive (high Conscientiousness), and

social (high Agreeableness) functioning

The presence of such emotional, cognitive, and social stability has important consequences in terms of psychological and well‐being outcome measures including

life satisfaction,

academic/professional achievement or

general health,

longevity, and

risk to develop dementia

Nevertheless, it remains unclear which are the neurobiological underpinnings of this behavioral stability and in particular whether they are dependent on the differences in intra‐cortical myelin and myelination.

3.3 Intra‐cortical myelin content in relation to each of the FFM personality traits

Neuroticism positively related to the intra‐cortical myelin content in the occipital cortex (Brodmann’s area 18/19)

At the same time, a significantly negative correlation was found between Neuroticism and the intra‐cortical myelin levels in the prefrontal cortex (PFC) pole (Brodmann’s area 10)

3.3.2 Extraversion

Extraversion was positively associated with the intra‐cortical myelin content in the superior parietal lobule (Brodmann’s area 7)

3.3.3 Openness

Openness was negatively associated with the intra‐cortical myelin content in the anterior cingulate cortex

3.3.4 Agreeableness

A positive relationship was found between Agreeableness and the intra‐cortical myelin content in the anterior orbitofrontal cortex (Brodmann’s area 11)

3.3.5 Conscientiousness

Conscientiousness positively related to the intra‐cortical myelin content in the PFC pole (Brodmann’s area 10) and negatively to the intra‐cortical myelin levels in the dorsal anterior cingulate cortex (Brodmann’s area 32)

Discussion

…these findings show that intra‐cortical myelin, as estimated via the MRI‐based T1/T2‐weighted contrast ratio, is a sensitive measure to investigate the neuroanatomical basis of the behavioral differences described by the FFM of personality.

Summary and conclusions

In conclusion, our results showed that intra‐cortical myelin is significantly linked to variability in personality traits.

Of note, most of the effects were localized in high‐order brain regions, a group of cortical areas with light myelin content and prolonged myelination, both at the phylogenetic and the ontogenetic levels.

This may depend on the fact that many of the FFM personality traits relate to high‐level cognitive and socio‐affective skills which have significantly evolved in human beings and that are critically mediated by the cito‐architectonically complex and lightly myelinated cortices.

Finally, the statistically robust relation between heterogeneity in the intra‐cortical myelin content and personality differences in healthy people suggests that the myelo‐architectural features may show even more pronounced changes in people with psychiatric illnesses such as major depressive disorders.

pj
(In defense of genuinely bright researchers that may in fact have some ‘real’ answers, they also likely know by now that what is discovered/found -and what’s published -are two entirely different things.)

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